A rapid and simple LC-MS/MS method for personalized busulfan dosing in pediatric patients undergoing hematopoietic stem cell transplantation (HSCT)

Background: Busulfan is commonly used as a conditioning regimen before hematopoietic stem cell transplantation (HSCT). There is a big inter-individual variability in busulfan exposure and the narrow therapeutic index, especially in pediatric population. Therefore, to achieve therapeutic efficacy and safety concurrently, personalized busulfan dosing, guided by pharmacokinetic study with serial plasma samples, is needed a few hours afterwards. Methods: A fast, sensitive, and accurate method for busulfan measurement was developed, validated, and implemented with liquid-chromatography-mass spectrometry (HPLC-MS/MS). The sample preparation procedure involves only protein precipitation and dilution, and the HPLC MS/MS method takes 3 min/sample. The assay was linear from 10 ng/ml to 7500 ng/ml (R-2 = 0.99). Recoveries were above 90%. The precision was determined at 3 levels (30, 300 and 4000 ng/ml): the intra-day variability (%CV) ranged from 1.4% to 2.5% (n = 20); the inter-day variability ranged from 2.2% to 5.5% (n = 20). The accuracy of the HPLC MS/MS test was evaluated with an old HPLC-fluorescence method (n = 84), and a Correlation Coefficient (R) of 0.99 was observed. Conclusions: The analytical performance of the assay allows for timely dose adjustment and has been implemented in clinical service for better clinical outcome.